1. Field of the Invention
The present invention generally relates to equipment which provides mobile communication, and more particularly, to mobile communication equipment and a mobile communication method by which load balancing is accomplished using an IPv6 Anycast Address scheme.
2. Discussion of Background
In recent years, the operation of mobile communication networks under Internet Protocol (IP) has been examined actively. Standardizing Mobile IPv6 specifications is underway by the Internet Engineering Task Force (IETF) (Ref. Mobility Support in IPv6 <draft-ietf-mobileiip-ipv6-18.txt>, Work in Progress).
Primary constituents of a network of Mobile IPv6 are a Mobile Node (MN), Home Agent (HA), and Correspondent Node (CN). The MN is assigned a unique IP address (home address) that remains unchanged as it moves. A link that has the same prefix as the home address is called a home link. One or more HAs can be placed on a home link. If a plurality of HAs exist on a same link, the HAs exchange information such as HA addresses and preferences in order to hold a list of the HAs on the link. For the information exchange, Router Advertisement messages are used.
When the MN moves to a link outside the home link, it gets its IP address on the foreign link. This address is called a Care of Address (hereinafter referred to as CoA). The MN receives router advertisement messages which are periodically transmitted by a router installed on the foreign link. By detecting a prefix that differs from the home address, the MN finds itself moved away from home.
When the MN finds itself moved away from home, it registers its current location with an HA. The MN is provided with a Home Agent Address Discovery function and capable of dynamically searching for the IP address of an HA.
The MN creates a Mobile IPv6 Home-Agents Anycast Address from the prefix of the home link. The MN sends an ICMP Home Agent Address Discovery Request message to the above address. The above message is transmitted to any HA on the home link. An HA that received the above message sends back an ICMP Home Agent Address Discovery Reply message including the HA information to the MN. By extracting the HA information from the above message, the MN gets the address of the HA. The MN carries out a Binding Update message to register its current location to the HA address it acquired.
Having received the Binding Update message, the HA stores the home address of the MN and binding information associated with the CoA to the Binding Cache. Then, the HA multicasts Gratuitous Neighbor Advertisement messages in order to capture a packet addressed to the above MN and operates as proxy for the above MN.
The CN is the correspondent node communicating with the MN.
A procedure in which the CN sends a packet to the MN will be described below.
The CN sends a packet to the home address of the MN. The HA captures the packet addressed to the home address of the MN. The HA searches the Binding Cache and gets a CoA associated with the home address of the MN. The HA attaches an IP header addressed to the CoA to the received packet (encapsulation) and sends the packet to the CoA.
When the MN receives the above packet addressed to the CoA, it detaches the previously attached IP header (decapsulation) so that the original packet is restored.
An address scheme of IPv6 is specified in RFC2373. In the address scheme of IPv6, three types are defined: unicast, anycast, and multicast. An anycast address designates a group of interfaces. A packet with an anycast address set for its destination address is sent to the nearest interface in the group of interfaces having the anycast address. As an example of anycast address usage, the above-mentioned Home Agent Address Discovery function of Mobile IP uses this address type.
When resolving a link-layer address associated with an anycast address, an IPv6 node sends Neighbor Solicitation messages to the multicast address of its neighboring nodes. A node that received the Neighbor Solicitation message, if its address is set for the target address parameter in this message, sends a Neighbor Advertisement message. In the Neighbor Advertisement message to an anycast address, an override flag is not set.
Area A and area B are interconnected and, when a mobile node (MN) falling within area A has moved to area B, an HA existing in area A and retaining the location information on the mobile node operates as proxy for the MN.
In some implementation, the HA consists of one or more servers and the load for MN location registration and packet forwarding is shared by the servers. In this case, it can be assumed that the servers are assigned a Mobile IPv6 Home-Agents Anycast Address.
When a router near to the HA receives a packet addressed to a Mobile IPv6 Home-Agents Anycast Address having the prefix of the HA, it searches the Neighbor Cache for the above Anycast Address. If the above Anycast Address does not exist in the Neighbor Cache, the nearby router sends Neighbor Solicitation messages to the neighboring nodes in order to resolve a link-layer address. The Neighbor Solicitation messages include the above Anycast Address in the target address field. The servers constituting the HA send back Neighbor Advertisement messages in reply to the Neighbor Solicitation message.
However, in the Neighbor Advertisement messages to the anycast address, an override flag is not set. Thus, the nearby router registers the link-layer address information for the server that first replied to the Neighbor Solicitation message into the Neighbor Cache. Consequently, the nearby router forwards the Home Agent Address Discovery Request message transmitted from the MN to the particular server registered in the Neighbor Cache. The MN receives a Home Agent Address Discovery Reply message including the HA information from the particular server. Because the MN registers its current location with the HA, based on the received information, MN location registration is concentrated on the particular server. Unfortunately, when the HA consists of one or more servers, a problem arises that the load for MN location registration and packet forwarding cannot be shared by the servers.